Liquid type identifying method and liquid type identifying device

ABSTRACT

A liquid type identifying method and device for correctly and quickly determining whether or not a liquid is a predetermined one. An identifying sensor unit ( 2 ) so disposed as to face a flow passage ( 24 ) of a liquid to be measured has an indirect-heating liquid type detecting section ( 21 ) including a heater and a heat sensor and a liquid temperature sensing section ( 22 ). A single pulse voltage is applied to the heater of the liquid type detecting section to allow the heater to generate heat, and an identification calculation section makes an identification according to the output of the liquid type detecting circuit including the heat sensor of the liquid type detecting section and the liquid temperature sensing section.

This application is a 371 of PCT/JP2005/008946 filed on May 17, 2005,published on Dec. 8, 2005 under publication number WO 2005/116620 A1which claims priority benefits from Japanese Patent Application Number2004-159334 filed May 28, 2004.

TECHNICAL FIELD

The present invention relates to a liquid type identifying method andliquid type identifying device which use thermal properties of liquid todetermine whether or not a liquid is a predetermined one.

A method and device for identifying liquid type according to the presentinvention can be used for determining whether or not a liquid that issprayed as urea solution having a predetermined urea concentration to anexhaust gas purification catalyst for decomposition of nitrogen oxide(NOx) in a system for purifying exhaust gas emitted from aninternal-combustion engine of, e.g., a car is actually the urea solutionhaving a predetermined urea concentration.

BACKGROUND ART

In an internal-combustion engine of a car, fossil fuels such as gasolineor light-oil are burned. Exhaust gas generated by the burning containswater and carbon dioxide, as well as environmental pollutants such asunburned carbon monoxide (CO), unburned carbon hydride (HC), sulfuroxide (SOx), and nitrogen oxide (NOx). In recent years, variouscountermeasures to purify the car exhaust gas have been taken especiallyfor environmental protection and prevention of living environmentpollution.

As one of such countermeasures, a use of an exhaust gas purificationcatalyst unit can be exemplified. Specifically, a three-way catalyst forexhaust gas purification is disposed in the middle of an exhaust system,and, there, CO, HC, NOx, etc. are decomposed by oxidation-reductionprocess to thereby render the above environmental pollutants harmless.In order to maintain the decomposition of NOx in the catalyst unit, ureasolution is sprayed to the catalyst from upstream side of the catalystunit in the exhaust system. In order to enhance the rate ofdecomposition of NOx, urea concentration of the urea solution shouldfall within a specified range, and a urea concentration of 32.5% isconsidered to be optimum.

The urea solution is stored in a urea solution tank installed in a car.In this state, however, concentration may change with time, orunevenness in the concentration distribution may locally occur in thetank. The urea solution which is supplied from the tank to a spraynozzle through a supply pipe by means of a pump is taken from the outletprovided near the bottom portion of the tank in general. Therefore, itis important for the urea solution in such an area to have apredetermined urea concentration, in order to enhance the efficiency ofthe catalyst unit.

Further, it could be that a liquid other than the urea solution isaccidentally introduced into the urea solution tank under presentcircumstances. In such a case, it is necessary to quickly detect thatthe liquid is a solution other than the urea solution having apredetermined urea concentration so as to issue an alarm, in order forthe catalyst unit to fulfill its capability.

Conventionally, measurement of the concentration of urea in the ureasolution has not directly been made. Meanwhile, a technique that usesNOx sensors disposed respectively on the upstream and downstream sidesof the catalyst unit in the exhaust system has been made. In thistechnique, it is determined whether optimum decomposition of NOx hasbeen carried out based on the difference in NOx concentration detectedby these sensors. However, this technique aims at measuring the effectof a reduction in the amount of NOx and therefore cannot determinewhether or not the liquid is urea solution having a predetermined ureaconcentration even at the beginning of the spray of urea solution aswell as before the spray. Further, the NOx sensor used in such atechnique did not have sufficient sensitivity for ensuring spray of ureasolution having a urea concentration falling within a predeterminedrange.

JP-A-11-153561 discloses a fluid identifying method. In this method, acurrent is applied to heat a heater, and the heat generated is used toheat a temperature sensor. Then, thermal influence is applied to heattransfer from the heater to temperature sensor using a fluid to beidentified and, based on an electrical output value of the temperaturesensor which corresponds to a resistance value, the type of the fluid tobe identified is determined. The application of a current to the heateris periodically performed in this method.

However, since the current application to the heater is periodicallyperformed (that is, current is applied with a large number of pulses) inthe fluid identifying method, it takes time to carry out theidentification processing. That is, it is difficult to identify the typeof a fluid at short times. Further, although this method can distinguishamong substances (e.g., water, air, and oil) having properties largelydifferent from each other using representative values, it has difficultydetermining whether or not the solution as described above is ureasolution having a predetermined urea concentration correctly andquickly.

DISCLOSURE OF INVENTION

The present invention has been made in view of the above situation, andan object thereof is to provide a liquid type identifying method andliquid type identifying device capable of determining whether or not aliquid is a predetermined one correctly and quickly.

To solve the above problem, according to the present invention, there isprovided

a liquid type identifying method, wherein a single pulse voltage isapplied to a heater disposed to face a liquid to be measured to allowthe heater to generate heat, and it is determined whether or not theliquid to be measured is a predetermined one based on a combination of aliquid-type-corresponding first voltage value corresponding to adifference between an initial temperature of a temperature sensordisposed to face the liquid to be measured and a first temperaturethereof obtained at the time point after a first time period has elapsedfrom a start of application of the single pulse voltage andliquid-type-corresponding second voltage value corresponding to adifference between the initial temperature of the temperature sensor anda second temperature thereof obtained at the time point after a secondtime period, which is longer than the first time period, has elapsedfrom the start of application of the single pulse voltage.

In an aspect of the present invention, it is determined that the liquidto be measured is the predetermined one only when both theliquid-type-corresponding first voltage value andliquid-type-corresponding second voltage value fall within theirrespective predetermined ranges and, otherwise, it is determined thatthe liquid to be measured is not the predetermined one. In an aspect ofthe present invention, the predetermined range of theliquid-type-corresponding first voltage value and that of theliquid-type-corresponding second voltage value change depending on atemperature of the liquid to be measured. In an aspect of the presentinvention, the liquid-type-corresponding first voltage value andliquid-type-corresponding second voltage value are obtained based onoutputs of a liquid type detecting circuit including both thetemperature sensor and a liquid temperature detecting section fordetecting a temperature of the liquid to be measured.

In an aspect of the present invention, an average initial voltage valuewhich is obtained by sampling an initial voltage predetermined number oftimes before the start of application of the single pulse to the heaterand averaging them is used as a voltage value corresponding to theinitial temperature of the temperature sensor, an average first voltagevalue which is obtained by sampling a first voltage at the time afterthe first time period has elapsed from the start of application of thesingle pulse to the heater predetermined number of times and averagingthem is used as a voltage value corresponding to the first temperatureof the temperature sensor, an average second voltage value which isobtained by sampling a second voltage at the time after the second timeperiod has elapsed from the start of application of the single pulse tothe heater predetermined number of times and averaging them is used as avoltage value corresponding to the second temperature of the temperaturesensor, a difference between the average first voltage value and averageinitial voltage value is used as the liquid-type-corresponding firstvoltage value, and a difference between the average second voltage valueand average initial voltage value is used as theliquid-type-corresponding second voltage value.

In an aspect of the present invention, the predetermined liquid is ureasolution having a urea concentration falling within a predeterminedrange. In an aspect of the present invention, a first calibration curveor second calibration curve indicating a relationship between thetemperature and liquid-type-corresponding first voltage value orliquid-type-corresponding second voltage value with respect to ureasolutions having different urea concentrations is prepared and, when theliquid to be measured is determined to be urea solution having a ureaconcentration falling within a predetermined range, the ureaconcentration of the urea solution is calculated based on an output of aliquid temperature detecting section for detecting the temperature ofthe liquid to be measured, liquid-type-corresponding first voltage valueor liquid-type-corresponding second voltage value, and first or secondcalibration curve.

To solve the above problem, according to the present invention, there isalso provided a liquid type identifying device for determining whether aliquid to be measured is a predetermined one, comprising:

an identifying sensor section disposed to face a flow passage of theliquid to be measured, the identifying sensor section having both anindirect-heating liquid type detection section including a heater andtemperature sensor and a liquid temperature detecting section fordetecting the temperature of the liquid to be measured; and

an identifying calculation section which applies a single pulse voltageto the heater of the indirect-heating liquid type detection section toallow the heater to generate heat and identifies the type of the liquidto be measured based on outputs of a liquid type detecting circuitincluding both the temperature sensor of the indirect-heating liquidtype detection section and the liquid temperature detecting section,

wherein the identifying calculation section determines whether or notthe liquid to be measured is the predetermined one based on acombination of a liquid-type-corresponding first voltage valuecorresponding to a difference between an initial temperature of thetemperature sensor and a first temperature thereof obtained at the timepoint after a first time period has elapsed from a start of applicationof the single pulse voltage and liquid-type-corresponding second voltagevalue corresponding to a difference between the initial temperature ofthe temperature sensor and a second temperature thereof obtained at thetime point after a second time period, which is longer than the firsttime period, has elapsed from the start of application of the singlepulse voltage.

In an aspect of the present invention, the predetermined liquid is ureasolution having a urea concentration falling within a predeterminedrange. In an aspect of the present invention, aliquid-temperature-corresponding output value corresponding to thetemperature of the liquid to be measured is input from the liquidtemperature detecting section to the identifying calculation section,and the identifying calculation section uses a first calibration curveor second calibration curve indicating a relationship between thetemperature of the liquid to be measured and liquid-type-correspondingfirst voltage value or liquid-type-corresponding second voltage valuewith respect to urea solutions having different urea concentrations tocalculate the urea concentration of the urea solution assuming that theliquid to be measured is the urea solution having a urea concentrationfalling within a predetermined range, and wherein the urea concentrationis calculated based on the liquid-temperature-corresponding output valueobtained with respect to the liquid to be measured,liquid-type-corresponding first voltage value orliquid-type-corresponding second voltage value, and first or secondcalibration curve.

In an aspect of the present invention, the indirect-heating liquid typedetection section and liquid temperature detecting section have a heattransfer member for liquid type detection section and a heat transfermember for liquid temperature detecting section for heat exchange withthe liquid to be measured, respectively.

In the present invention, with a single pulse voltage applied to aheater to allow the heater to generate heat, it is determined whether ornot the liquid to be measured is a predetermined one based on acombination of a liquid-type-corresponding first voltage valuecorresponding to a difference between the initial temperature of atemperature sensor and a first temperature thereof obtained at the timepoint after a first time period has elapsed from the start of the singlepulse voltage application and liquid-type-corresponding second voltagevalue corresponding to a difference between the initial temperature ofthe temperature sensor and a second temperature thereof obtained at thetime point after a second time period has elapsed from the start of thesingle pulse voltage application. Based on this method, it can bedetermined that the liquid to be measured is the predetermined one onlywhen both the liquid-type-corresponding first voltage value andliquid-type-corresponding second voltage value fall within theirrespective predetermined ranges and, otherwise, it can be determinedthat the liquid to be measured is not the predetermined one. Thus, it ispossible to determine whether or not the liquid to be measured is thepredetermined one correctly and quickly.

By appropriately changing the predetermined ranges of theliquid-type-corresponding first voltage value and that of theliquid-type-corresponding second voltage value depending on thetemperature of the liquid to be measured, it is possible to make theabove determination more correctly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view showing an embodiment of a liquidtype identifying device according to the present invention;

FIG. 2 is a partly omitted cross-sectional view of the liquid typeidentifying device of FIG. 1;

FIG. 3 is a view showing a state where the liquid type identifyingdevice has been set to a tank;

FIG. 4 is an enlarged view showing an indirect-heating liquid typedetection section and a liquid temperature detecting section;

FIG. 5 is a cross-sectional view showing the indirect-heating liquidtype detection section of FIG. 4;

FIG. 6 is an exploded perspective view showing a thin-film chip of theindirect-heating liquid type detection section;

FIG. 7 is a diagram showing a configuration of a circuit for liquididentification;

FIG. 8 is a diagram showing a relationship between a single pulsevoltage P applied to a heater and sensor output Q;

FIG. 9 is a diagram indicating that the liquid-type-corresponding firstvoltage value obtained using sugar solution having a certain sugarconcentration exists within the range of the liquid-type-correspondingfirst voltage value V01 obtained using urea solution having a ureaconcentration falling within a predetermined range;

FIG. 10 is a diagram in which both of the liquid-type-correspondingfirst voltage value V01 and liquid-type-corresponding second voltagevalue V02 obtained with respect to the urea solution, sugar solution andwater are represented by a relative value when the respective values V01and V02 of the urea solution having a urea concentration of 30% are setto 1.000;

FIG. 11 is a diagram showing an example of a first calibration curve;

FIG. 12 is a diagram showing an example of a second calibration curve;

FIG. 13 shows an example of a liquid-temperature-corresponding outputvalue T;

FIG. 14 is a graph schematically showing that criteria of thedetermination whether the liquid to be measured is a predeterminedliquid, which is performed using the combination ofliquid-type-corresponding first voltage value V01 andliquid-type-corresponding second voltage value V02, changes depending onthe temperature; and

FIG. 15 is a flowchart showing a liquid identifying process,

wherein reference numeral 2 denotes a liquid-type identifying sensorsection, 2 a base body, 2 b,2 c O-ring, 2 d cover member, 21indirect-heating liquid type detection section, 22 liquid temperaturedetecting section, 23 mold resin, 24 introduction passage for liquid tobe measured, 21 a thin-film chip, 21 b bonding material, 21 c,22 c metalfin, 21 d bonding wire, 21 e,22 c external electrode terminal, 21 a 1substrate, 21 a 2,22 a 2 temperature sensor, 21 a 3 interlayerdielectric film, 21 a 4 heater, 21 a 5 heater electrode, 21 a 6protection film, 21 a 7 electrode pad, 4 support portion, 4 a attachmentportion, 6 circuit substrate, 8 cover member, 10,14 wiring, 12connector, 64,66 resistor, 68 bridge circuit, 70 differential amplifier,71 liquid temperature detecting amplifier, 72 microcomputer, 74 switch,76 output buffer circuit, 100 urea solution tank, 102 opening, 104liquid type identifying device, 106 inlet piping, 108 outlet piping, 110urea solution supply pump, and US denotes a liquid to be measured.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described below withreference to the accompanying drawings.

FIG. 1 is an exploded perspective view showing an embodiment of a liquidtype identifying device according to the present invention. FIG. 2 is apartly omitted cross-sectional view of the liquid type identifyingdevice. FIG. 3 is a view showing a state where the liquid typeidentifying device has been set to a tank. In the present embodiment,urea solution having a urea concentration falling within a predeterminedrange is used as a predetermined solution.

As shown in FIG. 3, a urea solution tank 100 for NOx decomposition thatconstitutes an exhaust gas purification system installed in, e.g., a carhas, at its upper portion, opening 102. A liquid type identifying device104 according to the present invention is fitted to the opening 102. Theurea solution tank 100 is connected to both an inlet piping 106 throughwhich the urea solution is introduced into the tank and an outlet piping108 through which the urea solution is discharged from the tank. Theoutlet piping 108 is connected to the tank at substantially the sameheight position as the bottom line of the tank 100, and starts from theoutlet of the tank 100 to a not shown urea solution sprayer through aurea solution supply pump 110. In an exhaust system, the urea solutionis sprayed to a catalyst unit by the urea solution sprayer disposed inimmediately upstream side of an exhaust gas purification catalyst unit.

The liquid type identifying device 104 has an identifying sensor section(identifying sensor unit) 2 and support portion 4. The identifyingsensor section 2 is attached to one end (lower end) of the supportportion 4, and an attachment portion 4 a for attachment to the tankopening 102 is attached to the other end (upper end) of the supportportion 4.

The identifying sensor section 2 has an indirect-heating liquid typedetection section 21 including a heater and temperature sensor (heatsensor) and a liquid temperature detecting section (liquid temperaturesensing section) 22 for detecting the temperature of a liquid to bemeasured. The indirect-heating liquid type detection section 21 andliquid temperature detecting section 22 are disposed apart from eachother in vertical direction by a predetermined interval. FIG. 4 shows,in an enlarged manner, the indirect-heating liquid type detectionsection 21 and liquid temperature detecting section 22. FIG. 5 shows across-section of FIG. 4.

As shown in FIGS. 4 and 5, the indirect-heating liquid type detectionsection 21 and liquid temperature detecting section 22 are integratedwith each other by means of mold resin 23. As shown in FIG. 5, theindirect-heating liquid type detection section 21 has a thin-film chip21 a including the heater and temperature sensor, a metal fin 21 cserving as a heat transfer member for liquid type detection section,which is coupled to the thin-film chip 21 a by means of a bondingmaterial 21 b, and an external electrode terminal 21 e electricallyconnected respectively to electrodes of the heater and temperaturesensor of the thin-film chip 21 a by means of a bonding wire 21 d. Theliquid temperature detecting section 22, which has the sameconfiguration as that of the indirect-heating liquid type detectionsection 21, has a metal fin 22 c serving as a heat transfer member forliquid temperature detecting section and an external electrode terminal22 e.

FIG. 6 is an exploded perspective view showing the thin-film chip 21 aof the indirect-heating liquid type detection section 21. The thin-filmchip 21 a has a laminated body in which, for example, a substrate 21 a 1made of Al₂O₃, a temperature sensor 21 a 2 made of Pt, an interlayerdielectric film 21 a 3 made of SiO₂, a heater 21 a 4 made of TaSiO₂, aheater electrode 21 a 5 made of Ni, a protection film 21 a 6 made ofSiO₂, and an electrode pad 21 a 7 made of Ti/Au are sequentiallylaminated. Although not shown, the temperature sensor 21 a 2 is formedin a zig-zag pattern. Although a thin-film chip 22 a of the liquidtemperature detecting section 22 has the same configuration as that ofthe thin-film chip 21 a of the indirect-heating liquid type detectionsection 21, it does not allow the heater to be active, but allows only atemperature sensor 22 a 2 to be active.

As shown in FIGS. 1 and 2, the identifying sensor section 2 has a basebody 2 a attached to the lower end of the support portion 4. When thebase body 2 is attached to the support portion 4, O-rings 2 b areinterposed therebetween. A mold resin 23 integrating theindirect-heating liquid type detection section 21 and liquid temperaturedetecting section 22 is attached to the side surface of the base body 2a through an O-ring 2 c. A cover member 2 d is so provided to the basebody 2 a as to surround the metal fin 21 c for liquid type detectionsection and metal fin 22 c for liquid temperature detecting section. Ina state where the cover member 2 d has been attached to the base body 2a, an introduction passage 24 for liquid to be measured is formed. Theintroduction passage 24 extends, passing through the metal fin 21 c forliquid type detection section and metal fin 22 c for liquid temperaturedetecting section, in a vertical direction with its upper and lower endsopened. Further, in a state where the cover member 2 d has been attachedto the base body 2 a, the flange portion of the mold resin 23 is pressedagainst the base body 2 a to cause the mold resin 23 to be fixed to thebase body 21 a.

A circuit substrate 6 that constitutes a liquid type detecting circuitto be described later is disposed on the upper end of the supportportion 4. A cover member 8 is so attached to the upper end of thesupport portion 4 as to cover the circuit substrate 6. As shown in FIG.2, a wiring 10 electrically connecting the indirect-heating liquid typedetection section 21 and liquid temperature detecting section 22 of theidentifying sensor section 2 to the circuit substrate 6 extends insidethe support portion 4. A microcomputer that constitutes an identifyingcalculation section to be described later is mounted on the circuitsubstrate 6. A wiring 14 extends between the circuit substrate 6 and anexternal device through a connector 12 provided to the cover member 8for communication between them. The identifying calculation section maybe disposed outside the circuit substrate 6. In this case, the circuitsubstrate 6 and identifying calculation section are connected throughthe wiring 14.

The above-mentioned base body 2 a and cover member 2 d of theidentifying sensor section 2, support portion 4, and cover member 8 aremade of a corrosion-resistant material such as a stainless steel.

FIG. 7 shows a configuration of a circuit for liquid identificationperformed in the present embodiment. The temperature sensor 21 a 2 ofthe indirect-heating liquid type detection section 21, temperaturesensor 22 a 2 of the liquid temperature detecting section 22, and tworesistors 64, 66 constitute a bridge circuit 68. The output of thebridge circuit 68 is input to a differential amplifier 70, and theoutput of the differential amplifier 70 (also referred to as “liquidtype detecting circuit output” or “sensor output”) is input to themicrocomputer 72 that constitutes an identifying calculation sectionthrough a not shown A/D converter. Further, to the microcomputer 72, aliquid-temperature-corresponding output value which correspond to thetemperature of a liquid to be measured is input from the temperaturesensor 22 a 2 of the liquid temperature detecting section 22 through aliquid temperature detecting amplifier 71. Further, a heater controlsignal for controlling open/close of a switch 74 is output from themicrocomputer 72 to the switch 74 disposed in a power supplying line tothe heater 21 a 4 of the indirect-heating liquid type detection section21.

A liquid type identifying operation in the present embodiment will bedescribed below.

Firstly, the tank 100 is filled with a liquid to be measured US and, atthe same time, the introduction passage 24 for liquid to be measured,which is formed by the cover member 2 d of the identifying sensorsection 2, is filled with the liquid to be measured US. The liquid to bemeasured US supplied in the tank 100 and introduction passage 24 forliquid to be measured does not substantially flow.

The switch 74 is closed for a predetermined time period (e.g., 8seconds) by means of the heater control signal output from themicrocomputer 72 to the switch 74. Then, a single pulse voltage P havinga predetermined height (e.g., 10V) is applied to the heater 21 a 4 toallow the heater to generate heat. An output voltage (sensor output) Qof the differential amplifier 70 at that time gradually increases whilea voltage is applied to the heater 21 a 4 and gradually decreases afterthe voltage application to the heater 21 a 4 is ended, as shown in FIG.8.

As shown in FIG. 8, the microcomputer 72 samples the sensor outputs fora predetermined time period (e.g., 0.1 seconds) before the start ofvoltage application to the heater 21 a 4 a predetermined number of times(e.g., 256 times) and performs calculation for obtaining the averagevalue of the sensor outputs to thereby obtain an average initial voltagevalue V1. The average initial voltage value V1 corresponds to theinitial temperature of the temperature sensor 21 a 2.

Further, as shown in FIG. 8, the microcomputer 72 samples the sensoroutputs at the time point after a first time period (e.g., ½ or less ofthe single pulse application time (e.g., 0.5 to 3 seconds; 2 seconds inFIG. 8)), which is comparatively short time period, has elapsed from thestart of the voltage application to the heater (specifically,immediately before the elapse of the first time) a predetermined numberof times (e.g., 256 times) and performs calculation for obtaining theaverage value of the sensor outputs to thereby obtain an average firstvoltage value V2. The average first voltage value V2 corresponds to afirst temperature of the temperature sensor 21 a 2, which is obtained atthe time point after the first time period has elapsed from the start ofthe single pulse application. Then, a difference V01 (=V2−V1) betweenthe average initial voltage value V1 and average first voltage value V2is obtained as a liquid-type-corresponding first voltage value.

Further, as shown in FIG. 8, the microcomputer 72 samples the sensoroutputs at the time point after a second time period (e.g., single pulseapplication time (8 seconds in FIG. 8)), which is comparatively longtime period, has elapsed from the start of the voltage application tothe heater (specifically, immediately before the elapse of the secondtime) a predetermined number of times (e.g., 256 times) and performscalculation for obtaining the average value of the sensor outputs tothereby obtain an average second voltage value V3. The average secondvoltage value V3 corresponds to a second temperature of the temperaturesensor 21 a 2, which is obtained at the time point after the second timeperiod has elapsed from the start of the single pulse application. Then,a difference V02 (=V3−V1) between the average initial voltage value V1and average second voltage value V3 is obtained as aliquid-type-corresponding second voltage value.

A part of the heat generated in the heater 21 a 4 at the time of thesingle pulse voltage application is transferred to the temperaturesensor 21 a 2 through the liquid to be measured. This heat transferconsists primarily of two modes which differ from each other dependingon the time from the start of the pulse application. That is, at a firststage within a comparatively short time period (e.g., 3 seconds,especially 2 seconds) from the start of the pulse application, the hearttransfer is mainly controlled by conduction (therefore, theliquid-type-corresponding first voltage value V01 is mainly influencedby the heat conductivity of a liquid). At a second stage after the firststage, the heat transfer is mainly controlled by natural convection(therefore, the liquid-type-corresponding second voltage value V02 ismainly influenced by the kinetic viscosity of a liquid). It is becausethat, at the second stage, the natural convection occurs by the liquidheated at the first stage so that rate of the heat transfer by thenatural convection increases.

As described above, it is considered that the optimum concentration[percent by weight (this is the same in the following description)] ofthe urea solution used in the exhaust gas purification system is 32.5%.Therefore, the allowable range of the urea concentration of the ureasolution to be stored in the urea solution tank 100 can be set to, e.g.,32.5%±5%. The value (±5%) of the allowable range may appropriately bechanged. That is, in the present embodiment, the urea solution having aurea concentration of 32.5±5% is defined as a predetermined solution.

The liquid-type-corresponding first voltage value V01 andliquid-type-corresponding second voltage value V02 change as the ureaconcentration of the urea solution changes. Therefore, a range(predetermined range) of the liquid-type-corresponding first voltagevalue V01 and a range (predetermined range) of liquid-type-correspondingsecond voltage value V02, which correspond to the urea solution having aurea concentration of 32.5±5%, exist.

Even in the case of a liquid other than the urea solution, an outputwithin a predetermined range of the liquid-type-corresponding firstvoltage value V01 and output within a predetermined range of theliquid-type-corresponding second voltage value V02 may be obtained insome cases, depending on its concentration. In other words, even whenthe liquid-type-corresponding first voltage value V01 orliquid-type-corresponding second voltage value V02 falls within itspredetermined range, a liquid to be measured is not always thepredetermined urea solution. For example, as shown in FIG. 9, theliquid-type-corresponding first voltage value of sugar solution having asugar concentration of about 25%±3% exists within the range of theliquid-type-corresponding first voltage value V01 obtained using theurea solution having a urea concentration falling within thepredetermined range of 32.5%±5% (i.e., within a range of 32.5%±5% interms of the sensor's concentration value).

However, the value of liquid-type-corresponding second voltage value V02obtained using the sugar solution having the above sugar concentrationbecomes largely different from the liquid-type-corresponding secondvoltage value V02 obtained using the urea solution having a ureaconcentration falling within the predetermined range. That is, as shownin FIG. 10, although some sugar solutions having a sugar concentrationfalling within a range of 15% to 35%, including sugar concentrationrange of the above 25%±3%, overlap with the urea solutions having a ureaconcentration falling within the predetermined range in terms of theliquid-type-corresponding first voltage value V01, they largely differfrom the urea solutions having a urea concentration falling within thepredetermined range in terms of the liquid-type-corresponding secondvoltage value V02. Note that, in FIG. 10, both of theliquid-type-corresponding first voltage value V01 andliquid-type-corresponding second voltage value V02 are represented by arelative value when the values V01 and V02 of the urea solution having aurea concentration of 30% are set to 1.000. That is, by making adetermination whether the solution to be identified is a predeterminedsolution based on whether the solution to be identified falls within apredetermined range in terms of both the liquid-type-corresponding firstvoltage value V01 and liquid-type-corresponding second voltage valueV02, it is possible to certainly determine that the sugar solution isnot a predetermined solution.

Further, a liquid other than a predetermined solution may overlap withthe predetermined solution in terms of the liquid-type-correspondingsecond voltage value V02 in some cases. However, in this case, a liquidto be measured differs from the predetermined solution in terms of theliquid-type-corresponding first voltage value V01, so that it ispossible to certainly determine that the liquid to be measured is not apredetermined solution by the above determination.

As described above, in the present invention, identification of theliquid type is performed based on the fact that solutions differ fromeach other in terms of a combination of the liquid-type-correspondingfirst voltage value V01 and liquid-type-corresponding second-voltagevalue V02. That is, the liquid-type-corresponding first voltage valueV01 and liquid-type-corresponding second voltage value V02 areinfluenced by different properties, i.e., heat conductivity and kineticviscosity, so that the combination of the liquid-type-correspondingfirst voltage value V01 and liquid-type-corresponding second voltagevalue V02 varies depending on the solution type, which enables theliquid identification as described above. By narrowing the predeterminedrange of the urea concentration, it is possible to further increase theidentification accuracy.

In the embodiment of the present invention, a first calibration curveindicating a relationship between the temperature andliquid-type-corresponding first voltage value V01 and a secondcalibration curve indicating a relationship between the temperature andliquid-type-corresponding second voltage value V02 are previouslyobtained with respect to some urea solutions (reference urea solutions)each having a known urea concentration, and these calibration curves arestored in a storage means of the microcomputer 72. FIGS. 11 and 12 showexamples of the first and second calibration curves, respectively. Inthese examples, the calibration curves of reference urea solutionshaving urea concentrations c1 (e.g., 27.5%) and c2 (e.g., 37.5%) areshown.

As shown in FIGS. 11 and 12, the liquid-type-corresponding first voltagevalue V01 and liquid-type-corresponding second voltage value V02 changedepending on the temperature, so that when these calibration curves areused to identify a liquid to be measured, aliquid-temperature-corresponding output value T which is input from thetemperature sensor 22 a 2 of the liquid temperature detecting section 22through the liquid temperature detecting amplifier 71 is also used. FIG.13 shows an example of the liquid-temperature corresponding output valueT. Such a calibration curve is also stored in the storage means of themicrocomputer 72.

When the liquid-type-corresponding first voltage value V01 is measured,a temperature value is first obtained from theliquid-temperature-corresponding output value T of the liquid to bemeasured with reference to the calibration curve of FIG. 13. Theobtained temperature value is set as t. Then, on the first calibrationcurve of FIG. 11, the liquid-type-corresponding first voltage valuesV01(c1;t) and V01(c2;t) of the respective calibration curves whichcorrespond to the temperature value t are obtained. Subsequently, cx ofthe liquid-type-corresponding first voltage value V01(cx;t) obtainedwith respect to the liquid to be measured is determined by performingproportional calculation using the liquid-type-corresponding firstvoltage values V01(c1;t) and V01(c2;t) of the respective calibrationcurves. That is, cx is calculated from the following equation (1) basedon V01(cx;t), V01(c1;t), and V01(c2;t):

$\begin{matrix}{{cx} = {{c\; 1} + {{\left( {{c\; 2} - {c\; 1}} \right)\left\lbrack {{V\; 01\left( {{cx};t} \right)} - {V\; 01\left( {{c\; 1};t} \right)}} \right\rbrack}/\left\lbrack {{V\; 01\left( {{c\; 2};t} \right)} - {V\; 01\left( {{c\; 1};t} \right)}} \right\rbrack}}} & (1)\end{matrix}$

Similarly, when the liquid-type-corresponding second voltage value V02is measured, the liquid-type-corresponding second voltage valuesV02(c1;t) and V02(c2;t) of the respective calibration curves whichcorrespond to the temperature value t, which has been obtained asdescribed above, are obtained on the second calibration curve of FIG.12. Subsequently, cy of the liquid-type-corresponding second voltagevalue V02(cy;t) obtained with respect to the liquid to be measured isdetermined by performing proportional calculation using theliquid-type-corresponding second voltage values V02(c1;t) and V02(c2;t)of the respective calibration curves. That is, cy is calculated from thefollowing equation (2) based on V01(cy;t), V01(c1;t), and V01(c2;t):

$\begin{matrix}{{cy} = {{c\; 1} + {{\left( {{c\; 2} - {c\; 1}} \right)\left\lbrack {{V\; 02\left( {{cy};t} \right)} - {V\; 02\left( {{c\; 1};t} \right)}} \right\rbrack}/\left\lbrack {{V\; 02\left( {{c\; 2};t} \right)} - {V\; 02\left( {{c\; 1};t} \right)}} \right\rbrack}}} & (2)\end{matrix}$

When the first and second calibration curves of FIGS. 11 and 12 arecreated based on the liquid-temperature-corresponding output value T inplace of the temperature, the storage of the calibration curve of FIG.13 and conversion using the same can be omitted.

As described above, a predetermined range that changes depending on thetemperature can be set with respect, respectively, to theliquid-type-corresponding first voltage value V01 andliquid-type-corresponding second voltage value V02. By setting c1 to27.5% and c2 to 37.5% as described above, it can be seen that a regionbetween the two calibration curves in each of FIGS. 11 and 12corresponds to the predetermined liquid (i.e., urea solution having aurea concentration of 32.5%±5%).

FIG. 14 is a graph schematically showing that the criteria of thedetermination whether the liquid to be measured is a predeterminedliquid, which is performed using the combination ofliquid-type-corresponding first voltage value V01 andliquid-type-corresponding second voltage value V02, changes depending onthe temperature. As the temperature rises (t1, t2, t3 in this order), aregion in which a liquid to be measured is determined to be apredetermined liquid is moved (AR(t1), AR(t2), AR(t3) in this order).

FIG. 15 is a flowchart showing a liquid type identifying processperformed by the microcomputer 72.

Firstly, N=1 is stored in the microcomputer 72 (S1) before applicationof a pulse voltage to the heater 21 a 4 which is performed under heatercontrol. Then, the microcomputer 72 samples sensor outputs to obtain theaverage first voltage value V1 (52). After that, the microcomputer 72starts heater control and samples sensor outputs at the time after thefirst time period has elapsed from the start of the voltage applicationto the heater 21 a 4 to obtain the average first voltage value V2 (S3).Then, microcomputer 72 calculates V2−V1 to obtain theliquid-type-corresponding first voltage value V01 (S4). Subsequently,microcomputer 72 samples sensor outputs at the time after the secondtime period has elapsed from the start of the voltage application to theheater 21 a 4 to obtain the average second voltage value V3 (S5). Then,microcomputer 72 calculates V3−V1 to obtain theliquid-type-corresponding second voltage value V02 (S6).

Then, referring to the temperature value t obtained with respect to theliquid to be measured, the microcomputer 72 determines whether acondition that both the liquid-type-corresponding first voltage valueV01 and liquid-type-corresponding second voltage value V02 fall withintheir respective predetermined ranges at the corresponding temperatureis satisfied (S7). When determining in S7 that at least one of theliquid-type-corresponding first voltage value V01 andliquid-type-corresponding second voltage value V02 does not fall withinits predetermined range (NO in S7), the microcomputer 72 determineswhether the stored value N is 3 (S8). When determining that N is not 3[i.e., the current measurement routine is not the third routine(specifically, the current routine is the first or second routine)] (Noin S8), the microcomputer 72 increases the stored value N by 1 (S9) andreturns to S2. On the other hand, when determining in S8 that the storedvalue N is 3 [i.e., the current measurement routine is the thirdroutine] (YES in S8), the microcomputer 72 determines that the liquid tobe measured is not a predetermined one (S10).

On the other hand, when determining in S7 that both theliquid-type-corresponding first voltage value V01 andliquid-type-corresponding second voltage value V02 fall within theirrespective predetermined ranges (YES in S7), the microcomputer 72determines that the liquid to be measured is a predetermined one (S11).

In the present embodiment, after S1, the urea concentration of the ureasolution is calculated (S12). The urea concentration can be calculatedbased on the output of the liquid temperature detecting section 22,i.e., temperature t obtained with respect to the liquid to be measured,liquid-type-corresponding first voltage value V01, and first calibrationcurve of FIG. 11 and by using the above equation (1). Alternatively, theurea concentration can be calculated based on the output of the liquidtemperature detecting section 22, i.e., temperature t obtained withrespect to the liquid to be measured, liquid-type-corresponding secondvoltage value V02, and second calibration curve of FIG. 12 and by usingthe above equation (2).

In the manner as described above, identification of the liquid type canbe performed correctly and quickly. The routine of the liquid typeidentification can appropriately be performed when a car engine startsup, or periodically, or at the time of a request from a driver or car(ECU to be described later), or key-off time. Further, it is possible tomonitor in a desired mode whether or not a liquid in the urea solutiontank is urea solution having a predetermined urea solution. A signal(signal indicating whether a liquid to be measured is a predeterminedone, as well as, the urea concentration, in the case where the liquid tobe measured is a predetermined one [=urea solution having apredetermined urea concentration]) indicating the liquid type obtainedas described above is output to an output buffer circuit 76 shown inFIG. 7 through a not shown D/A converter. The signal is then output asan analog output from the output buffer circuit 76 to a not shown maincomputer (ECU) which performs car engine combustion control. An analogoutput voltage value corresponding to the liquid temperature is alsooutput to the main computer (ECU). A signal indicating the liquid typecan be taken out as a digital output according to need, and can be inputto a device that performs display, alarm, and other operations.

Further, an alarm may be issued when it is detected that the temperatureof the urea solution is decreased near to the freezing temperature(about −13° C.) of the urea solution based on theliquid-temperature-corresponding output value T input from the liquidtemperature detecting section 22.

The liquid type identification described above uses natural convectionand uses a principle that there is a correlation between the kineticviscosity of a liquid to be measured such as urea solution and sensoroutput. In order to enhance the accuracy of the liquid identification,it is preferable to make a forced flow due to an external factor lesslikely to occur in the liquid to be measured around the fin 21 c forliquid type detection section and fin 22 c for liquid temperaturedetecting section. In this regard, it is preferable to use the covermember 2 d, especially, one that forms the vertical introduction passagefor liquid to be measured. The cover member 2 d functions also as aprotection member for preventing foreign matters from contacting theindirect-heating liquid type detection section 21 and liquid temperaturedetecting section 22.

Although the urea solution having a predetermined urea concentration isused as a predetermined fluid in the embodiment described above, apredetermined liquid may be a solution using a dissolved substance otherthan urea or other liquids.

1. A liquid type identifying method, which identifies whether or not aliquid to be measured which is an aqueous solution contains apredetermined solute by sensing heat generated by energization with atemperature sensor, the identification of whether or not the liquid tobe measured contains a predetermined solute being made based on acombination of a liquid-type-corresponding first voltage valuecorresponding to a difference between an initial temperature of thetemperature sensor and a first temperature thereof obtained at the timepoint after a first time period has elapsed from a start of theenergization and a liquid-type-corresponding second voltage valuecorresponding to a difference between the initial temperature of thetemperature sensor and a second temperature thereof obtained at the timepoint after a second time period, which is longer than the first timeperiod, has elapsed from the start of the energization.
 2. The liquidtype identifying method as set forth in claim 1, wherein thepredetermined solute is a urea.
 3. The liquid type identifying method asset forth in claim 1, wherein the liquid-type-corresponding firstvoltage value and liquid-type-corresponding second voltage value areobtained based on outputs of a liquid type detecting circuit includingboth the temperature sensor and a liquid temperature detecting sectionfor detecting a temperature of the liquid to be measured.
 4. The liquidtype identifying method as set forth in claim 1, wherein an averageinitial voltage value which is obtained by sampling an initial voltagepredetermined number of times before the start of energization to theheater and averaging them is used as a voltage value corresponding tothe initial temperature of the temperature sensor, an average firstvoltage value which is obtained by sampling a first voltage at the timeafter the first time period has elapsed from the start of energizationto the heater predetermined number of times and averaging them is usedas a voltage value corresponding to the first temperature of thetemperature sensor, an average second voltage value which is obtained bysampling a second voltage at the time after the second time period haselapsed from the start of energization to the heater predeterminednumber of times and averaging them is used as a voltage valuecorresponding to the second temperature of the temperature sensor, adifference between the average first voltage value and average initialvoltage value is used as the liquid-type-corresponding first voltagevalue, and a difference between the average second voltage value andaverage initial voltage value is used as the liquid-type-correspondingsecond voltage value.
 5. The liquid type identifying method as set forthin claim 1, which identifies whether or not the liquid to be measuredwhich is an aqueous solution contains a predetermined solute in apredetermined concentration based on a combination of theliquid-type-corresponding first voltage value and theliquid-type-corresponding second voltage value.
 6. The liquid typeidentifying method as set forth in claim 5, wherein a first calibrationcurve or second calibration curve indicating a relationship between thetemperature and liquid-type-corresponding first voltage value orliquid-type-corresponding second voltage value with respect to ureasolutions having different urea concentrations is prepared and, when theliquid to be measured is determined to be urea solution having a ureaconcentration falling within a predetermined range, the ureaconcentration of the urea solution is calculated based on an output of aliquid temperature detecting section for detecting the temperature ofthe liquid to be measured, liquid-type-corresponding first voltage valueor liquid-type-corresponding second voltage value, and first or secondcalibration curve.
 7. The liquid type identifying method as set forth inclaim 5, wherein it is determined that the liquid to be measured is anaqueous urea solution containing urea in a predetermined concentrationonly when both the liquid-type-corresponding first voltage value andliquid-type-corresponding second voltage value fall within respectivepredetermined ranges and, otherwise, it is determined that the liquid tobe measured is not an aqueous urea solution containing urea in apredetermined concentration.
 8. The liquid type identifying method asset forth in claim 7, wherein the predetermined range of theliquid-type-corresponding first voltage value and that of theliquid-type-corresponding second voltage value change depending on atemperature of the liquid to be measured.
 9. The liquid type identifyingmethod as set forth in claim 1, wherein the energization is applied byapplying a single pulse voltage and the heat generated by theenergization is transferred through the liquid to be measured to thetemperature sensor disposed to face the liquid.
 10. The liquid typeidentifying method as set forth in claim 9, wherein the single pulsevoltage is applied to a heater disposed to face the liquid to bemeasured.
 11. A liquid type identifying device, which identifies whetheror not a liquid to be measured which is an aqueous solution contains apredetermined solute by sensing heat generated by energization with atemperature sensor, the device comprising: an identifying sensor sectiondisposed to face a flow passage of the liquid to be measured, theidentifying sensor section having both a liquid type detection sectionincluding the temperature sensor and a liquid temperature detectingsection for detecting the temperature of the liquid to be measured; andan identifying calculation section which identifies the type of theliquid to be measured based on outputs of a liquid type detectingcircuit including both the temperature sensor and the liquid temperaturedetecting section, wherein the identifying calculation sectiondetermines whether or not the liquid to be measured is an aqueoussolution of a predetermined solute based on a combination of aliquid-type-corresponding first voltage value corresponding to adifference between an initial temperature of the temperature sensor anda first temperature thereof obtained at the time point after a firsttime period has elapsed from a start of the energization and aliquid-type-corresponding second voltage value corresponding to adifference between the initial temperature of the temperature sensor anda second temperature thereof obtained at the time point after a secondtime period, which is longer than the first time period, has elapsedfrom the start of the energization.
 12. The liquid type identifyingdevice as set forth in claim 11, wherein the predetermined solute is aurea.
 13. The liquid type identifying device as set forth in claim 11,wherein the liquid type detection section and liquid temperaturedetecting section have a heat transfer member for liquid type detectionsection and a heat transfer member for liquid temperature detectingsection for heat exchange with the liquid to be measured, respectively.14. The liquid type identifying device as set forth in claim 11, whereinthe identifying calculation section determines whether or not the liquidto be measured which is an aqueous solution contains a predeterminedsolute in a predetermined concentration based on a combination of theliquid-type-corresponding first voltage value and theliquid-type-corresponding second voltage value.
 15. The liquid typeidentifying device as set forth in claim 14, wherein aliquid-temperature-corresponding output value corresponding to thetemperature of the liquid to be measured is input from the liquidtemperature detecting section to the identifying calculation section,and the identifying calculation section uses a first calibration curveor second calibration curve indicating a relationship between thetemperature of the liquid to be measured and liquid-type-correspondingfirst voltage value or liquid-type-corresponding second voltage valuewith respect to urea solutions having different urea concentrations tocalculate the urea concentration of the urea solution assuming that theliquid to be measured is the urea solution having a urea concentrationfalling within a predetermined range, and wherein the urea concentrationis calculated based on the liquid-temperature-corresponding output valueobtained with respect to the liquid to be measured,liquid-type-corresponding first voltage value orliquid-type-corresponding second voltage value, and first or secondcalibration curve.
 16. The liquid type identifying device as set forthin claim 11, wherein the energization is applied by applying a singlepulse voltage and the heat generated by the energization is transferredthrough the liquid to be measured to the temperature sensor disposed toface the liquid.
 17. The liquid type identifying device as set forth inclaim 16, wherein the identifying sensor section includes a heater, andthe single pulse voltage is applied to the heater.